Yeah, but virtually all of the manufacturers have this policy, simply because they have no idea what type of additive you might put into it. So it's either a policy of "no additives," or having to test and qualify particular additives for approval, or be willing to pay a warranty bill no matter what anyone tosses into the fuel....

agreed, but biodiesel does appear to be an acceptable additive for diesel per the manual. It just is not going to help the cetane much with a max concentration of 5%.